Hello!
I am a new user of stata. I have a problem of exporting the
covariance-variance of estimate (after regress) to a external file with
extension, such as csv (or any data format with comma as seperation). The
command 'outsheet' is not working for this. Can someone tell me how to do
this? Thank you!

To copy a the columns of variance-covariance matrix to a set of variables,
use the -svmat- command on the matrix -e(V)- created by an estimation
command. The new variables can then be output using -outsheet- like any
other variables. See -[P] matrix mkmat- in the Stata programming manual.

and this should create a set of variables -vvector1-, -vvector2- and
-vvector3-, which are output to a file -vv1.csv-.

If James wants to output estimates and/or confidence intervals and/or
P-values to a spreadsheet, rather than a covariance matrix, then he might
like to find out about the -parmest- package, which saves estimation output
as a Stata data set. In Web-aware Stata, type -ssc describe parmest- to
find out more, and type -ssc install parmest- to install the -parmest-
package over the Web from the SSC site.